One of the most misunderstood aspects of US tariffs is stacking — the way tariffs from different legal authorities add up on the same import. After the SCOTUS ruling struck down IEEPA tariffs and replaced them with 10% Section 122, and with steel/aluminum doubled to 50%, the stacking math has changed significantly. Understanding tariff stacking is essential for accurate cost calculations.
What Is Tariff Stacking?
Tariff stacking occurs when multiple tariff programs apply simultaneously to the same import. Each tariff comes from a different legal authority and is assessed independently. The US currently has three main tariff regimes that can stack: Section 122 tariffs (10% flat for all countries, effective Feb 24, 2026), Section 232 tariffs (50% steel/aluminum, 50% copper, 25% autos, 25% semiconductors), and Section 301 tariffs (7.5-100% on Chinese goods). When a product falls under multiple programs, you pay all of them — they don't replace each other, they add up.
Real-World Stacking Examples (Post-SCOTUS)
Chinese steel articles: 50% Section 232 + 25% Section 301 = 75% total duty — Section 122 does NOT stack on the Section 232 metal content. Chinese electric vehicles: 10% Section 122 + 100% Section 301 = 110%. Chinese solar panels: 10% Section 122 + 50% Section 301 = 60%. Vietnamese steel articles: 50% Section 232 (Section 122 is excluded on the metal). German automobiles: 25% Section 232 auto (Section 122 is excluded on Section 232 goods). Japanese steel articles: 50% Section 232. UK steel: 25% Section 232 (EPD rate). The key pattern: goods already subject to Section 232 (steel, aluminum, copper, autos) are carved out of the Section 122 surcharge to the extent the 232 duty applies — Section 122 reaches only any non-metal content. Section 301 and the MFN base rate, by contrast, do stack.
Anti-Stacking Rule: Section 232 Goods Are Excluded from Section 122
The most important anti-stacking rule is general, not country-specific: goods already subject to a Section 232 tariff (steel, aluminum, copper, automobiles) are NOT also charged the 10% Section 122 surcharge to the extent the Section 232 duty applies. So a car subject to the 25% Section 232 auto tariff pays 25%, not 25% + 10%, and an article wholly of steel pays its 50% Section 232 rate, not 60%. Section 122 reaches only any non-metal content of a Section 232 article. (On top of this, USMCA-qualifying vehicles, steel, and aluminum from Canada and Mexico can avoid the Section 232 tariff entirely.)
USMCA Exemption: Canada/Mexico Steel/Aluminum
Separately, USMCA-qualifying steel and aluminum from Canada and Mexico can be exempt from the Section 232 steel/aluminum tariff (50%) altogether. Non-USMCA Canadian steel pays 50% Section 232 — and because Section 232 goods are excluded from the Section 122 surcharge on their metal content, the rate is 50%, not 60%. The UK pays a reduced 25% Section 232 rate on metal articles under the Economic Prosperity Deal.
Why Effective Rates Differ from Announced Rates
When tariff rates are discussed in the media or in trade negotiations, the number cited is usually just one component. 'A 10% tariff under Section 122' doesn't include Section 232 (50% on steel) or Section 301 (25-100% on Chinese goods). Always calculate the full stacked rate for your specific product and country combination. The difference between the headline rate and the effective rate can be 25-75 percentage points or more.
Key Takeaway
Tariff stacking means your actual duty rate is often 2-8x the headline number. China steel at 85%, Chinese EVs at 110%, and Vietnamese steel at 60% are common examples. Always check all three tariff programs (Section 122, Section 232, Section 301) for your product. USMCA and UK EPD offer limited relief on certain products.
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